This invention relates to image forming apparatuses such as copiers and printers provided with a plurality of sheet transport routes for transporting a sheet after an image fixation along a certain transport route of the plurality of transport routes and a route changer mechanism for selectively changing the transport route.
A construction of an image forming apparatus as shown in FIG. 3 is known in which a sheet after an image transfer is transported along a certain transport route of a plurality of transport routes and discharged outside a main body of the apparatus by an operation of a route changer mechanism.
FIG. 3 is a partially enlarged diagram of the construction. In FIG. 3, 302 is an imaging unit of the apparatus. The imaging unit 302 includes a photoreceptor 300 and a transfer roller 301. An image transfer is performed by the imaging unit 302.
Specifically, an electrostatic latent image is formed on an outer circumference of the photoreceptor 300 based on an image read from a document. By electrically attracting charged toner onto the latent image, the latent image is developed into a toner image on the surface of the photoreceptor 300. The toner image on the photoreceptor surface is electrically attracted to a copy sheet transported to the photoreceptor 300 due to a transfer voltage applied between the photoreceptor 300 and the transfer roller 301 to transfer the toner image onto the copy sheet. In this way, the toner image is transferred onto the sheet.
Fixing rollers 303, 303 are arranged downstream of the imaging unit 302 with respect to a sheet transport direction (indicated by the upward-directing arrow in FIG. 3). After passing the imaging unit 302, the sheet has the toner image fixed thereon by the fixing rollers 303, 303 by a thermal treatment. The fixing rollers 303, 303 are accommodated in a frame 303a composed of a resin or a metallic material together with a heater as a one-piece unit. The construction of the one-piece unit contributes to improvement of heat transmission efficiency.
A transport route formed downstream of the fixing rollers 303, 303 is branched into a transport route 305 communicating with a discharge port 307 and a transport route 304 communicating with a discharge port 308 opposite to the discharge port 307. A sheet after an image fixation is selectively transported either along the transport route 304 or the transport route 305 by the route changer mechanism.
Specifically, a switching member 306 as the route changer mechanism is provided at the junction of the transport routes 304, 305. The switching member 306 is pivotable about a pivot point to selectively guide a sheet after an image fixation to the transport route 304 and the transport route 305. When the switching member 306 is set in a state shown by the solid line in FIG. 3, the sheet is transported toward the transport route 305 while guided along the bold solid line P in FIG. 3 and discharged onto a discharge tray 313 via the discharge port 307. In this case, the sheet is discharged onto the discharge tray 313 with the side carrying an image facing downward.
On the other hand, when the switching member 306 is set in a state shown by the dashed line in FIG. 3, the sheet is transported toward the transport route 304 and discharged onto a finisher (not shown) or a discharge tray (not shown) with the side carrying an image facing upward.
Also, when the switching member 306 is set in the dashed-line state in FIG. 3 to guide a sheet along the transport route 304, the transport routes 304, 305 are communicated to each other. Accordingly, in this state, the transport routes 304, 305 functions as a switchback route to guide a sheet toward the discharge port 308 along the phantom line P' in FIG. 3 by performing the following operations.
Specifically, first, the switching member 306 is set in the solid-line state to temporarily transport a sheet toward the discharge port 307. When a tail end of the sheet reaches a certain position between a discharge roller pair 309, 309 provided near the discharge port 307 and the switching member 306, the discharge roller 309 is driven in a reverse direction. At this time, changing the posture of the switching member 306 to the dashed-line state allows the sheet to be transported toward the discharge port 304 along the transport routes 305, 304.
More specifically, in the above state when the switchback route is provided by the transport routes 304, 305, connecting the transport route 304 to an access route (not shown) via the discharge port 308 and the imaging unit 302 enables a double sided image transfer by feeding the sheet after a first image transfer again to the imaging unit 302 while utilizing the switchback route and the access route. The access route connecting the transport route 304 and the imaging unit 302 may be provided by mounting an external device on a side wall of the apparatus main body, e.g., a side wall of the apparatus on the same side as a cover 310 in which the discharge port 308 is formed.
The cover 310 is openably mounted on the side wall of the apparatus, and opening the cover 310 allows the transport route 304 accessible to outside of the apparatus. Likewise, a cover 311 is openably mounted on a top portion of the apparatus near the discharge port 307. Opening the cover 311 allows the transport route 305 to be accessible to outside of the apparatus. Opening the cover 310 (311) enables removing a jammed sheet in the transport route 304 (305).
In the above apparatus, in case of removing a jammed sheet in the transport route 304 (305), it is likely that the switching member 306 may be broken or damaged due to a pulling force exerted thereto. In such a case, it is required to replace the broken or damaged switching member 306 with a new one.
Since the route changer mechanism including the switching member 306 is directly mounted on the apparatus main body, a service person must take out the broken or damaged switching member 306 by inserting his/her hand inside the apparatus main body. As shown in FIG. 3, however, around the switching member 306 there are densely arranged a number of parts such as discharge rollers 312, 312 for feeding a sheet to the transport route 304 and the fixing rollers 303, 303 in a certain limited space, which makes a replacement cumbersome. In particular, it is highly likely that a new switching member 306 is mounted to the apparatus main body at a position deviated from the previous mounting position with respect to the fixing rollers 303, 303. Mounting at the deviated position obstructs securing the transport route for a sheet which has passed between the fixing rollers 303, 303 and is being transported toward the transport route 304 (305), thereby increasing the possibility of jamming.
There is an idea of providing a sufficient space in the apparatus for facilitating the replacement of the switching member 306 in order to improve serviceability of the apparatus. This idea, however, leads to production of a large sized apparatus and not favorable in a practical sense.
Accordingly, there is demanded an improved arrangement of the apparatus with improved serviceability of the route changer mechanism such as easy replacement of a switching member to eliminate a sheet transport failure due to a positional displacement of the route changer mechanism relative to the fixing rollers while effectively suppressing production of a large sized apparatus.